The present disclosure relates generally to cases in gas turbine engines and more specifically to fan case liners and methods for attaching such liners.
Aircraft turbine and turbofan engines include a set of fan blades that rotate within a fan case immediately downstream from an inlet cowl. The fan case is constructed to cover and protect the fan blades and to contain the fan blades in the event that a foreign object, such as a bird, is ingested through the inlet cowl. A liner is often installed on the inner surface of the fan case to acoustically reduce the noise emitted by the engine and to improve the efficiency of the engine by reducing clearance gaps between the fan blades and the fan casing.
In the prior art, one method of installing the liner onto the inner surface of the fan case is to bond the liner to the inner surface by an adhesive or epoxy. Bonding the liner to the inner surface of the fan case is disadvantageous because it is difficult to subsequently remove the bonded liner from the inner surface of the fan case for repair or replacement. In addition, the bonded liner is subject to movement caused by the thermal contraction and expansion of the fan casing during engine operation. This is especially problematic when the fan casing is made of a different material with a different coefficient of thermal expansion than the fan blades. During cold engine operations at high altitudes, a fan case with a different coefficient of thermal expansion than the fan blades could contract less than the fan blades, causing gaps to form between the fan blades and the bonded liner and thereby allow air to leak around the fan blade tips and decrease the efficiency of the engine.
In the prior art, fan case liners have also been connected to the inner surface of the fan case by bolts that extended radially through the fan case and the liner. While the bolted liner is easier to remove from the fan case than the bonded liner, the bolted liner is also subject to the thermal contraction and expansion of the fan casing during engine operation, similar to the bonded liner as described above. In addition, the bolted liner requires additional machining to ensure that the heads of the bolts do not extend radially inward from the bolted liner and disrupt the flowpath of the gases moving across the fan blades. Additional machining of the bolted liner increases the manufacturing complexity and cost of the bolted liner.